Method and apparatus for radio resources management in multi-radio access technology wireless systems

ABSTRACT

Methods and apparatus for performing wireless communication in a wireless transmit/receive unit (WTRU) configured for multi-radio access technology (RAT) operation are disclosed. A method includes the WTRU wirelessly communicating information on a first operating frequency according to a first RAT. The WTRU also wirelessly communicates information on a second operating frequency according to a second RAT.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/513,180, which was filed on Jul. 29, 2011, the contents of which arehereby incorporated by reference herein.

BACKGROUND

Demand for improved network coverage, improved capacity and increasingbandwidth for voice and data services in wireless systems has led tocontinuous development of a number of radio access technologies (RATs).Examples of such RATs include, for example, Global Systems Mobile (GSM),Wideband Channel Division Multiple Access (WCDMA), High-Speed PacketAccess (HSPA) (which may include High-Speed Downlink Packet Access(HSDPA) and High-Speed Uplink Packet Access (HSUPA) with theirrespective multicarrier counterparts), Long Term Evolution (LTE) (whichmay include support for carrier aggregation in LTE Release 10 andbeyond) in the Third Generation Partnership Project (3GPP), IEEE802.11b/a/g/n, IEEE 802.16a/e, IEEE 802.20, Code Division MultipleAccess 2000 1x (CDMA2000 1x) and cdma2000 Evolution-Data Optimized(cdma200 EV-DO) in the Third Generation Partnership Project 2 (3GPP2).

SUMMARY

Methods and apparatus for performing wireless communication in awireless transmit/receive unit (WTRU) configured for multi-RAT operationare disclosed. A method includes the WTRU wirelessly communicatinginformation on a first operating frequency according to a first RAT andwirelessly communicating information on a second operating frequencyaccording to a second RAT.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a block diagram of an example system for multi-RATcommunication;

FIG. 3 is a block diagram of an example control plane for multi-RAToperation using a single RRC instance and a single RRC connection perWTRU;

FIG. 4 is a flow diagram of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 3;

FIG. 5 is a block diagram of an example control plane for multi-RAToperation using an RRC instance for each configured RAT and a single RRCconnection per WTRU;

FIG. 6 is a flow diagram of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 5;

FIG. 7 is a block diagram of an example control plane for multi-RAToperation using an RRC instance and an RRC connection for eachconfigured RAT;

FIG. 8 is a flow diagram of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 7; and

FIG. 9 is a block diagram illustrating the E-UTRA RRC states andmobility support between E-UTRAN, UTRAN and GERAN.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

As RATs such as WCDMA and LTE have developed, they have been made toenable use of more than one component carrier (CC) for transmissions andreceptions between a WTRU and a base station. A CC may be, for example,a frequency on which a WTRU operates. For example, a WTRU may receivetransmissions on a downlink (DL) CC, which may comprise a plurality ofDL physical channels. For another example, a WTRU may performtransmissions on an uplink (UL) CC, which may comprise a plurality of ULphysical channels.

A cell typically minimally includes a DL CC which may be linked to a ULCC based on the SI received by the WTU that is either broadcast on theDL CC or using dedicated configuration signaling from the network. Forexample, when the SI is broadcast on the DL CC, the WTRU may receive theUL frequency and bandwidth of the linked UL CC as part of the SI IE(e.g., when in RRC_IDLE for LTE or when in idle/CELL_FACH for WCDMA(i.e., when the WTRU does not yet have an RRC connection to thenetwork).

More specifically, 3GPP WCDMA Release 8 provided support forsimultaneous use of two HSDPA component carriers (2C-HSDPA), Release 9provided support for MIMO in multicarrier DL WCDMA and also introducedsupport for two HSUPA UL CCs, and Release 10 introduced support for upto four DL CCs (4C-HSDPA). For Release 11, the number of DL CCs may beincreased to eight (8C-HSDPA). 3GPP LTE Release 10 introduced supportfor simulaneous transmission and/or reception using the radio resourcesof a plurality of CCs between a base station and a mobile terminalwithin the same transmission interval. The transmission time interval(TTI) for HSPA is a 2 ms subframe, and the TTI for 3GPP LTE Releases 8,9 and 10 is a 1 ms subframe (each radio frame (10 ms) includes 10equally sized sub-frames of 1 ms).

Network architectures for different Rats may support different networkfunctionalities at different entities within the architecture. For someRATs, similar functionalities (e.g., MAC functionalities) may beperformed by different entities within the same architecture, andrchitectures for different RATs may include different entities. Forexample, for UTRAN, the radio resource control (RRC), packet datacontrol protocol (PDCP), radio link control (RLC), medium access controldedicated (MAC-d) and MAC-is sub-layers are located in the radio networkcontroller (RNC), while medium access control high speed (MAC-hs), MAC-iand layer 1 (L1) are located in the Node B. Further, for universalterrestrial radio access network (UTRAN), security (e.g. ciphering),segmentation and reassembly services to MAC, as well as in-orderdelivery services to PDCP, are provided by the RLC, while MAC ensuresordering between the hybrid automatic repeat request (HARQ) processesfor the RLC layer. For evolved UTRAN (eUTRAN), for another example,there is no RNC, and the RRC, PDCP, RLC and MAC layers are all locatedin the eNodeB (eNB). Security (e.g., ciphering, integrity andauthentication) and in-order delivery services (e.g., at handover) areprovided by the PDCP, while the RLC provides segmentation,re-segmentation and reassembly services to MAC.

One of the design objectives for LTE release 8 was to allow operators todeploy LTE using the same sites as for legacy WCDMA deployments toreduce deployment and radio planning costs. Accordingly, networkoperators may deploy both WCDMA/HSPA and LTE in the same coverage areas,LTE deployments may have similar coverage as existing WCDMA/HSPAdeployments and multi-mode WTRUs supporting both WCDMA/HSPA and LTEaccesses may be widely deployed.

However, spectrum is a costly resource, and not all frequency bands maybe available to all operators. Thus, while it is expected that operatorsmay offer support for both HSPA and LTE services, carrier aggregationscenarios may be limited to at most 2-3 component carriers per RAT for agiven operator. In addition, legacy deployments may be maintained forthe foreseeable future while LTE is being deployed, which may lead to asituation where operators see periods of underutilization of radioresources/spectrum and capacity in one of their RATs.

HSPA Release 10 with MIMO offers downlink peak data rates of 42 Mbps,and Release 10 multicarrier HSPA may further increase the peak rate byintroducing support for up to four DL CCs. LTE Releases 8 and 9 offer upto 100 Mbps in the single CC DL, and LTE Release 10 with intra-RATcarrier aggregation may further increase the peak rate by combiningtransmission resources of up to 5 CCs. Some motivations for takingadvantage of the combined data rates/capacity of the multi-RATdeployment may include, for example, reducing the cost of offeringhigher data rates (data enhancement scenario), migrating from WCDMA/HSPAto LTE with limited spectrum available (migration scenario), maximizingusage of deployed RATs (e.g., through load balancing), and maximizingusage of radio components in the WTRU (e.g., dual-band receiver).

In addition to capitalizing on increased peak rates, an operator maywant to reserve a frequency band for other reasons (e.g., for home eNBdeployment). Further, combining HSPA resources with LTE resources mayadditionally provide means for ensuring service continuity (e.g., eitherfor circuit switched (CS) Voice and/or for services requiring LTE datarates). Accordingly, it may be desirable to have methods allowing a WTRUto operate simultaneously on multiple frequencies, where the WTRUoperates on at least one of the frequencies according to a differentRAT.

Embodiments described herein may relate to multi-mode WTRUs supportingsimultaneous (or near-simultaneous) operation on CCs of a plurality ofdifferent RATs. Embodiments described herein may also relate to howmulti-mode WTRUs may perform radio resource management and related RRCprocedures when using different RATs. In an embodiment, the WTRUs mayperform radio resource management and related RRC procedures usingdifferent RATs on different frequencies.

Some embodiments described herein are described with respect to thefirst RAT being LTE and the second RAT being WCDMA, HSUPA and/or HSDPA,and vice versa. However, the embodiments described herein may beapplicable to any wireless technology. Further, while not explicitlydescribed herein, embodiments described herein may be applicable toWTRUs that transmit using different RATs only in different timeintervals (i.e., some form of time division operation on a TTI basis) ondifferent frequencies and/or where such transmissions are performed inthe same frequency band.

FIG. 2 is a block diagram of an example system 200 for multi-RATcommunication. The illustrated system 200 includes a WTRU 204 and twobase stations (e.g., eNBs) 202 and 206. In FIG. 2, one WTRU 204 is incommunication with two base stations 202 and 206 using channels 208,210, 212 and 214. The channels 208, 210, 212 and 214 may be anycombination of UL and DL channels of any number of different RATs.

A multi-RAT operation may include any multi-mode WTRU simultaneouslyconfigured for operation with at least one CC of a first RAT (e.g., a DLCC, a UL CC, or one or more serving cell(s)) and with at least one CC ofa second RAT (e.g., a DL CC, a UL CC, or one or more serving cell(s)).The operation on the different CCs may occur either simultaneously, ornear-simultaneously in time. Operation according to different RATs mayalso be used sequentially, for example, on the same CC. A multi-modeWTRU may include any mobile terminal supporting a plurality of RATs,such as, for example, any combination of GSM, WCDMA, HSPA, HSDPA, HSUPA,LTE, IEEE 802.11b/a/g/n, IEEE 802.16a/e, IEEE 802.20, cdma2000 1x andcdma2000 EV-DO.

A serving cell may include, for example, a primary cell (PCell) or asecondary cell (SCell). More specifically, for a WTRU that is notconfigured with any SCell or that does not support operation on multipleCCs (carrier aggregation), there may be only one serving cell (thePCell). For a WTRU that is configured with at least one SCell, theserving cells may include a set of one or more cells comprising allconfigured PCell(s) and all configured SCell(s).

In an embodiment, the WTRU 204 may wirelessly communicate information ona first operating frequency according to a first RAT and may wirelesslycommunicate information on a second operating frequency according to asecond RAT. The communications on the first and second operatingfrequencies may occur over any combination of the channels 208, 210, 212and 214. For example, the WTRU 204 may wirelessly communicateinformation on a first operating frequency according to a first RAT(e.g., LTE) over a DL channel 208 (e.g., LTE DL) and may wirelesslycommunicate information on a second operating frequency according to asecond RAT (e.g., WCDMA) over a DL channel 212 (e.g., WCDMA HSDPA). Foranother example, the WTRU 204 may wireless communicate information on afirst operating frequency according to a first RAT (e.g., WCDMA) over aUL channel 212 (e.g., WCDMA HSUPA) and may wirelessly communicateinformation on a second operating frequency according to a second RAT(e.g., LTE) over a UL channel 214 (e.g., LTE UL).

A WTRU, such as the WTRU 204 illustrated in FIG. 2, may be configuredfor multi-RAT operation. A WTRU that supports access to a plurality ofRATs may access those resources using one of a number of differentcontrol plane arrangements and any one of a number of different methodssuch as, for example, the control planes and methods illustrated anddescribed below with respect to FIGS. 3-8.

FIG. 3 is a block diagram of an example control plane 300 for multi-RAToperation using a single RRC instance 302, a single state machine 304, asingle RRC connection 306 per WTRU, and one or more SRBs 308. Whenreferred to hereafter, the term RRC instance may conceptually represent,without limiting to possible additional aspects or a subset of thefollowing aspects, the use of an RRC protocol that may comprise a singlestate machine operating using a plurality of RRC states (e.g., CONNECTEDor IDLE for the LTE RRC protocol) with corresponding state transitions,RRC procedures (including related timers) including RRC control andmeasurement procedures, RRC PDUs and information elements (IEs), the RRCconfiguration (including parameters for configuration of RRC, PDCP, RLC,MAC), and the physical (PHY) layer. In the example illustrated in FIG.3, the single RRC instance 302 may handle the management of radioresources for all configured RATs.

For HSPA, there are at least four RRC states: CELL_DCH, CELL_FACH,CELL_PCH/URA_PCH and UTRA_IDLE. For LTE, there are at least two RRCstates: RRC_CONNECTED and RRC_IDLE. The WTRU is in RRC_CONNECTED when anRRC Connection has been established. Otherwise, the WTRU is in RRC_IDLE.

In the RRC_IDLE state, the WTRU at least monitors the paging channel todetect incoming calls, change of SI, and, in an embodiment, earlyterrestrial warning system (ETWS)/commercial mobile alert system (CMAS)notifications, and performs neighboring cell measurements, cellselection, cell re-selection, and SI acquisition. In the RRC_CONNECTEDstate, the WTRU may transmit/receive on unicast channels and at leastmonitor the paging channel and/or SI Block Type 1 to detect incomingcalls, change of SI, and, in an embodiment, ETWS/CMAS notifications. TheWTRU may also be configured with one or most secondary cells in additionto the primary cell.

For each of the RRC protocols described in the above paragraph, a set ofstates, transitions, messages (e.g., protocol data units (PDUs)) andprocedures are defined. FIG. 9 is a block diagram 900 illustrating theE-UTRA (e.g., LTE) RRC states including, for example., the CELL_DCHstate 902, the CELL_FACH state 904, the CELL_PCH and URA_PCH states 906,the UTRA_IDLE state 908, the E-UTRA RRC CONNECTED state 910, the E-UTRARRC IDLE state 912, the GSM_Connected state 914, the GPRS packettransfer mode 916 and the GSM Idle/GPRS Packet Idle State 918. FIG. 9also illustrates mobility support between E-UTRAN, UTRAN and GERAN.

In an embodiment, the single RRC instance 302 may manage the single RRCConnection 306, which may be used to handle radio resources managementfor all configured serving cells of any RAT. According to thisembodiment, there may be at most one RRC instance and one RRC connectionper WTRU at any time.

FIG. 4 is a flow diagram 400 of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 3. In the example illustrated inFIG. 4, a WTRU may first access a network and establish the RRCconnection 306 in a first RAT (e.g., a primary RAT (PRAT)) using the RRCinstance 302 (402). The WTRU may subsequently receive a configurationthat adds at least one serving cell of a second RAT (e.g., a secondaryRAT (SRAT) over the RRC connection 306 (404). The WTRU may thenconfigure the radio resources using the single RRC instance 302 (406).

A primary cell (PCell) may include, for example, a cell operation on aprimary frequency in which the WTRU performs the initial access to thesystem (e.g., the cell in which the WTRU performs the initial connectionestablishment procedure, the cell in which the WTRU initiates theconnection re-establishment procedure, or the cell indicated as theprimary cell in the handover procedure). The PCell may also correspondto a frequency indicated as part of the RRC configuration procedure.Some functions may be only supported on the PCell. For example, the ULCC of the PCell may correspond to the CC whose physical UL controlchannel resources are configured to carry all HARQacknowledgement/non-acknowledgement (ACK/NACK) feedback for a givenWTRU. For example, in LTE, the WTRU may use the PCell to derive theparameters for the security functions and for upper layer SI such asNon-Access Stratum (NAS) mobility information. Other functions that maybe supported only on the PCell DL may include SI acquisition and changemonitoring procedures on the broadcast channel (BCCH) and paging. Forexample, the PCell of WCDMA may be similar to the PCell of LTE. Asecondary cell (SCell) may include, for example, a cell operating on asecondary frequency, which may be configured once an RRCconnection isestablished and may be used to provide additional radio resources. SIrelevant for operation in the concerned S Cell may be provided usingdedicated signaling when the S Cell is added to the WTRU'sconfiguration. Although the parameters may have different values thanthose broadcast on the DL of the concerned S Cell using the SIsignaling, this information may be referred to as SI of the concerned SCell independently of the method used by the WTRU to acquire thisinformation.

A primary RAT (PRAT) (or anchor RAT) may include the radio accessnetwork technology. At least one serving cell may be configured as thePCell for the PRAT. The PCell may support at least one of establishing afirst RRC connection, deriving security parameters (e.g., in case asingle security context is used), using UL resources to transmit ULcontrol information (UCI) (e.g., if UCI is transmitted only on a servingcell of a first RAT), and/or configuring at least one serving cell withUL resources (e.g., if UL resources are configured only in a first RAT).Consequently, in some embodiments, the PRAT, or the anchor RAT, may alsobe referred to as the first RAT. A secondary RAT (SRAT) (or non-anchorRAT) may include the RAT for which none of the configured servingcell(s) is for the PRAT of the WTRU's configuration.

In an embodiment, a WTRU may access an LTE cell and establish an RRCconnection 306 with LTE as the PRAT using the corresponding RRCconnection establishment procedure. The WTRU may be configured using theRRC connection reconfiguration procedure of the PRAT with additionalserving cells, which may include one or more HSPA serving cells as theSRAT. In an embodiment, the RRC connection reconfiguration procedure maybe performed only once the security is activated in the PRAT. Further,in an embodiment, the WTRU may receive an RRC message including one ormore IEs pertaining to the HSPA configuration (e.g., SI configurationIEs, radio bearer IEs, transport channel IEs and physical channel IEs)during the RRC reconfiguration procedure.

In another embodiment, a WTRU may access an HSPA cell and establish anRRC connection 306 with HSPA as the PRAT using the corresponding RRCconnection establishment procedure. The WTRU may be configured using theRRC connection reconfiguration procedure of the PRAT with additionalserving cells (e.g., one or more LTE serving cells) as the SRAT. In anembodiment, the WTRU may be configured using the RRC Radio bearer setupprocedures of the PRAT to configure the PRAT specific information andsimultaneously configured the WTRU with SRAT serving cells.Alternatively, the WTRU may be configured with the SRAT in the RRCConnection Setup using the signaling radio bearer (SRB) of the PRAT. Inan embodiment, the RRC connection reconfiguration procedure may beperformed only once the security is activated in the PRAT. Further, inan embodiment, the WTRU may receive an RRC message including one or moreIEs pertaining to the LTE configuration (e.g., SI configuration IEsand/or RRC IEs, which may include at least one of a MAC-MainConfig IE, aCQI-ReportConfig IE, a PDSCH-Config IE, a PhysicalConfigDedicated IE, aRadioResourceConfigDedicated IE, and/or a RadioConfigCommon IE for theDL configuration of a serving cell and/or at least one of a PUSCH-ConfigIE and/or a SoundingRS-UL-Config IE for the UL configuration of theserving cell) during the RRC reconfiguration procedure.

SRBs are radio bearers used only for the transmission of RRC and NASmessages. SRB0 is used for RRC messages using the common control channel(CCH) logical channel. SRB1 is for RRC messages (e.g., with apiggybacked NAS message) and for NAS messages prior to establishment ofSRB2 using the dedicated control channel (DCCH) logical channel. SRB2 isfor NAS messages and is always configured after activation of security.Once security is activated, all RRC messages on SRB1 and SRB2 may beintegrity protected and ciphered.

When CCs (or serving cells) of different RATs are aggregated andconfigured for a given WTRU, it may, thus, be necessary to have methodsto handle the management of radio resource connections. In particular,if a plurality of RRC connections and/or state machines (SMs) may beused for multi-RAT access (e.g., one per RAT on which the WTRUoperates), it may be desirable to define methods to ensure properhandling of each RRC connection and possible interactions in between.Alternatively, if a single RRC connection and/or state machine may beused for multi-RAT access, it may be desirable to define methods bywhich a single RRC state machine can control a plurality of radioresources.

FIG. 5 is a block diagram of an example control plane 500 for multi-RAToperation using an RRC instance for each configured RAT, a state machinefor each RRC instance and a single RRC connection per WTRU. Morespecifically, the illustrated example includes an RRC instance 502 for aPRAT, a state machine 504 for the PRAT, an RRC instance 508 for an SRAT,a state machine 506 for the SRAT, a single RRC connection 510 and one ormore SRB(s) 512. In the example illustrated in FIG. 5, radio resourcesfor a plurality of RATs (e.g., the PRAT and the SRAT) may be managedusing a plurality of RRC instances (e.g., a single instance of thecontrol plane per configured RAT).

In an embodiment, the RRC instance 508 for the SRAT comprises a subsetof the RRC protocol for the concerned RAT. For example, the RRC instance508 for the SRAT may handle at least some radio resource managementfunctions for the corresponding RAT (e.g., intra-frequency andinter-frequency measurement configuration and reporting, radio linkmonitoring (RLM), SI maintenance and error handling). In an embodiment,the RRC instance 508 for each SRAT may interact with the RRC instance502 for the PRAT. In the illustrated embodiment, the RRC instance 502manages the single RRC connection 510, which may be used to handle radioresources management of at least one RAT. There is also an additionalRRC instance for each additional configured RAT (e.g., the RRC instance508 for the SRAT), which may comprise a subset of the RRC protocol forthe concerned RAT (SRAT).

For an LTE serving cell, a WTRU may perform RLM and determine UL radiolink failure (RLF) when it reaches the maximum number of preambletransmissions for the random access procedure and/or repeated failure toperform the random access procedure on the concerned serving cell.Further, for an LTE serving cell, a WTRU may determine DL RLF when theRRC instance receives number N310 consecutive out-of-synch indicationsfrom the physical (PHY) layer and a timer T310 subsequently expireswhile the WTRU has not recovered from the error condition that startedthe timer.

FIG. 6 is a flow diagram 600 of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 5. In the example illustrated inFIG. 6, a WTRU may first access a network and establish the RRCconnection 510 in a first RAT (e.g., PRAT) using a first RRC instance(RRC instance 502 for the PRAT) (602). The WTRU may subsequently receivea configuration that adds at least one serving cell of a second RAT(e.g., the SRAT) over the RRC connection 510 (604). The WTRU may thenuse a second RRC instance (RRC instance 508 for the SRAT), which mayconfigure the radio resources of the SRAT, using the RRC PDU(s) (e.g.,received over different SRBs) and/or configuration information receivedover the RRC connection 510 (606). In an embodiment, the second RRCinstance 508 may initially operate according to an RRC connected mode(e.g., LTE CONNECTED or HSPA CELL_DCH). The states of the RRC instancefor an SRAT may not be active, or the RRC connected mode may beinitiated by the PRAT.

For example, a WTRU may access an LTE cell and establish a RRCconnection with LTE as the PRAT using the corresponding RRC connectionestablishment procedure. The WTRU may be configured with additionalserving cells, for example, including one or more HSPA serving cells asthe SRAT. In an embodiment, the configuration procedure may be performedonly once the security is activated in the PRAT.

In an embodiment, the configuration may be received via the RRCconnection reconfiguration procedure of the PRAT. In an embodiment, theWTRU may receive an RRC message including one or more IEs pertaining tothe HSPA configuration, which may include, for example, at least one ofSI configuration IEs, radio bearer IEs, transport channel IEs, physicalchannel IEs, and secondary serving HS-DSCH IEs during the RRCreconfiguration procedure. In an embodiment, the RRC instance of thePRAT may forward the received configuration information of the SRAT tothe RRC instance of the corresponding SRAT, which may configure thecorresponding radio resources of the SRAT.

In another embodiment, the configuration may be received over an SRBconfigured such that it is associated with the RRC instance 508 of theSRAT. In an embodiment, the WTRU may receive an RRC PDU of the RRCprotocol of the SRAT over the SRB. In an embodiment, the RRC message mayinclude one or more IEs pertaining to the HSPA configuration, which mayinclude, for example, at least one of SI configuration IEs, radio bearerIEs, transport channel IEs, and physical channel IEs. In an embodiment,the RRC instance of the SRAT may perform the corresponding configurationprocedures, such as a radio bearer control procedure and a physicalchannel configuration procedure.

For example, a WTRU may access an HSPA cell and establish an RRCconnection with HSPA as the PRAT using the corresponding RRC connectionestablishment procedure. The WTRU may be configured with additionalserving cells, which may include, for example, one or more LTE servingcells as the SRAT. In an embodiment, this configuration procedure may beperformed only once the security is activated in the PRAT.

In an embodiment, the configuration may be received over the RRCconnection reconfiguration procedure of the PRAT. In an embodiment, theWTRU may receive an RRC message including one or more IEs pertaining tothe LTE configuration, which may include, for example, at least one ofSI configuration IEs, RRC IEs (which may include at least one of aMAC-MainConfig IE, CQI-ReportConfig IE, PDSCH-Config IE,PhysicalConfigDedicated IE, RadioResourceConfigDedicated IE, andRadioConfigCommon IE for the DL configuration of a serving cell and mayalso include at least one of a PUSCH-Config IE and SoundingRS-UL-ConfigIE for the UL configuration of the serving cell). In an embodiment, theRRC instance 502 of the PRAT may forward the received configurationinformation of the SRAT to the RRC instance of the corresponding SRAT,which may configure the corresponding radio resources of the SRAT.

In another embodiment, the configuration may be received over an SRBconfigured such that it is associated with the the RRC instance 508 ofthe SRAT. In an embodiment, the WTRU may receive an RRC PDU of the RRCprotocol of the SRAT over the SRB. In an embodiment, the RRC message mayinclude one or more IEs pertaining to the LTE configuration, which mayinclude, for example, at least one of SI configuration IEs, radioresource control IEs (e.g., including at least one of a MAC-MainConfigIE, CQI-ReportConfig IE, PDSCH-Config IE, PhysicalConfigDedicated IE,RadioResourceConfigDedicated IE, and a RadioConfigCommon IE for the DLconfiguration of a serving cell and at least one of a PUSCH-Config IEand a SoundingRS-UL-Config IE for the UL configuration of the servingcell). In an embodiment, the RRC instance of the SRAT may perform thecorresponding RRC reconfiguration procedure(s), such as a radio resourceconfiguration procedure.

FIG. 7 is a block diagram of an example control plane 700 for multi-RAToperation using an RRC instance for each configured RAT, a state machinefor each RRC instance, and an RRC connection for each configured RAT.More specifically, the illustrated example includes an RRC instance 702for a PRAT, a state machine 704 for the PRAT, an RRC instance 708 for anSRAT, a state machine 706 for the SRAT, an RRC connection 710 for thePRAT, an RRC connection 712 for the SRAT and one or more SRB(s) 714. Inthe example illustrated in FIG. 7, radio resources for a plurality ofRATs (e.g., the PRAT and the SRAT) may be managed using a plurality ofRRC instances (e.g., a single instance of the control plane perconfigured RAT).

FIG. 8 is a flow diagram 800 of an example method of performing wirelesscommunication in a WTRU configured for multi-RAT operation correspondingto the embodiment illustrated in FIG. 7. In the example illustrated inFIG. 8, a WTRU may establish the first RRC connection 710 in the firstRAT (e.g., the PRAT) using the first RRC instance 702 (802). The WTRUmay also establish the second RRC connection 712 in the second RAT(e.g., the SRAT) using the second RRC instance 708 (804).

In the embodiment illustrated in FIG. 7, each RRC instance 702 and 708manages a single RRC connection 710 and 712 for its respectiveconfigured serving cell(s) of the concerned RAT.

In an embodiment, the RRC connections 710 and 712 may be establishedaccording to any number of different methods. In an embodiment, a WTRUmay receive RRC signaling from the network on an existing RRCconnection. The RRC signaling may include, for example, a request toestablish an additional RRC connection to an SRAT, parameters touniquely identify a concerned cell (e.g., a frequency (DL and UL), acell identity, and SI). In another embodiment, the WTRU may receive anRRC reconfiguration message from the network on an existing RRCconnection that adds at least one serving cell for an SRAT. The RRCreconfiguration message may include, for example, parameters to uniquelyidentify a concerned cell (e.g., a frequency (DL and UL), a cellidentity, and SI). In another embodiment, when a packet data protocol(PDP) context is established for a new application, the WTRU may receivea request to establish an additional RRC connection to an SRAT. Inanother embodiment, a WTRU may autonomously initiate an access to a cellof a second RAT while it is already connected to a first RAT. Thisembodiment may be used, for example, where the WTRU supports multi-RATaccess using two independent RRC instances.

The WTRU may autonomously initiate the access to the cell of the secondRAT, for example, in response to receiving a paging message on a RATwhile the WTRU is camping on a cell with an RRC instance in idle mode.Alternatively, a WTRU may autonomously initiate an access to a cell of asecondary RAT on a condition that it determines that an application isrequesting service. For example, if the WTRU wants to initiate a CScall, and if it determines that it is a multi-RAT capable WTRU, it mayinitiate access to a cell in the secondary RAT and, in an embodiment,indicate the reason in the RRC connection establishment. In anotherembodiment, the WTRU may send a request to the network over the PRATindicating that it may initiate the setup of the SRAT (e.g., following aWTRU specific trigger). The WTRU may send the request to the network,for example, in response to receiving a certain service request, and, inan embodiment, indicate a reason in the RRC message sent over the PRAT.In this embodiment, the WTRU may wait for an explicit setup message fromthe network to instantiate the SRAT RRC connection.

In an embodiment, there may be no interaction between the RRC instances702 and 708. This may apply, for example, where a multi-mode WTRUoperates as a multi-homed IP device (e.g., where each RAT may correspondto a different IP interface from a network connectivity perspective),which may be configured using NAS procedures. More specifically, theWTRU may be seen by the network as a single device implementing twodifferent IP network interfaces, and, in an embodiment, each with itsown PDP context (i.e., IP address), control/user data paths, andsecurity context. RRM, mobility management, scheduling, and admissioncontrol for each RRC connection may be independent from each other.

In another embodiment, there may be additional interactions between theRRC instances 702 and 708. For example, an RRC message on a first RRCconnection (e.g., 702) may initiate a procedure by the WTRU by which theWTRU may perform at least one of entering an idle mode state, performingthe cell selection procedure to determine a suitable cell to camp on (oralternatively camp on a cell of a frequency indicated in the said RRCmessage), acquire the SI, monitor a paging channel, and perform anaccess to the SRAT. Alternatively, it may immediately perform an initialaccess to a cell, either selected by the WTRU using the cell selectionprocedure or, alternatively, to a cell of a frequency indicated in theRRC message.

In an embodiment, parameters may be exchanged or may be common to aplurality of RRC instances, including at least one of securityparameters, NAS configuration (including PDP context), and user planeparameters (if a single data path is used). For example, from a networkconnectivity perspective, the WTRU may still be seen as a single deviceimplementing a single IP network interface with a single PDP context(i.e., IP address), a single data path, and a single security context.The necessary parameter may be common to all RRC instances and obtained,for example, from the PRAT connection and/or the initial NASconfiguration. In an embodiment, RRM and mobility management for eachRRC connection may be configured independently from one another.Alternatively, mobility may be based on the PRAT connection (e.g., 710).

In an embodiment, the WTRU may be configured with zero or more SCellsfor the PRAT.

For the embodiments described with respect to FIGS. 5-8 wherein thecontrol plane includes a separate RRC instance for each configured RATfor radio resource management, the different RRC instances may interactwith one another using any one of a number of different methods, forexample, for security configuration, security activation, securityfailure, failure handling, reconfiguration of an RRC connection, RLM,error recovery, state transition, transaction back to idle mode andaction upon PUCCH/SRS release requests.

With respect to security configuration, activation and failure, the WTRUmay use a second RRC instance when it adds a first serving cell for anSRAT. In an embodiment, on a condition that security is activated foranother RRC instance, the WTRU may consider that security is alreadyactivated for the second RRC instance and apply the same configurationfor integrity protection and ciphering for the access stratum, whenapplicable.

With respect to failure handling, the WTRU may receive control planeinformation (e.g., an RRC PDU or an IE) for the RRC instance of an SRAT,which it may fail to process. On a condition that the WTRU receivescontrol plane information for the RRC instance of an SRAT that it failsto process, the WTRU may indicate to the network that the configurationfailed, suspend any ongoing transmission on a serving cell of theconcerned SRAT, invalidate the configuration for all servicing cells ofthe SRAT, remove the configuration for all serving cells of the SRAT,indicate to the network that the configuration failed and/or terminatethe secondary RAT RRC instance or secondary RAT RRC connection. On acondition that the WTRU receives a configuration message that adds,modifies or removes at least part of a configuration for at least oneserving cell of the SRAT, the WTRU may not successfully apply theconcerned configuration. In this case, the WTRU may invalidate theconfiguration of the concerned serving cell, remove the configuration ofthe concerned serving cell, invalidate the configuration for all servingcells of the SRAT, remove the configuration for all serving cells of theSRAT, indicate to the network that the configuration failed and/orterminate the SRAT RRC instance or secondary RAT connection. Any ofthese failures may not impact the operation and/or configuration of theRRC connection for the PRAT.

With respect to reconfiguring an RRC connection, the WTRU may receive aradio resource reconfiguration message that adds a configuration for afirst LTE serving cell with configured UL resources. The WTRU maysubsequently initiate a procedure to gain UL timing synchronization(e.g., a random access procedure on the UL PRACH resources of the cell).In an embodiment, the WTRU may receive a handover command, which mayinclude a configuration with at least one LTE serving cell withconfigured UL resources. In this embodiment, in addition to the initialaccess to the HSPA target cell, the WTRU may also initiate a procedureto gain UL timing synchronization (e.g., a random access procedure onthe UL PRACH resources of the LTE target cell).

With respect to RLM, a WTRU may perform RLM for configured serving cellsof an SRAT. In an embodiment, the WTRU may determine that it isexperiencing RLF, for example, according to the criterion for RLF of aserving cell of the corresponding RAT. When a WTRU determines RLF (DL orUL) for a serving cell of a first RAT, the WTRU may remove theconfiguration for all serving cells of the first RAT, turn off the radiofront end for the first RAT and/or indicate to the network of the RLFcondition for the concerned serving cell. In an embodiment, the RRCinstance of a first RAT may indicate the UL RLF condition to the RRCinstance of a second RAT.

With respect to state transition and related procedures, a change of RRCstate in a first RRC instance may trigger a change in state and/or aprocedure in a second RRC instance. For example, a state transition in afirst RRC instance may trigger a state transition in a second RRCinstance, a release of the RRC connection in a second RRC instance,and/or the WTRU may turn off the radio front end for a second RATcorresponding to a second RRC instance. In an embodiment, an RRC statetransition from CELL_DCH to any other state for an HSPA RRC instance maytrigger an LTE RRC instance to perform a state transition to RRC_IDLE,release the RRC LTE connection and/or turn off the LTE front end. Forexample, if HSPA is the PRAT, LTE may be the SRAT and UL resources maynot be configured for the LTE RAT. In another embodiment, an RRC statetransition to idle mode in a first RAT may trigger a state transition tothe idle mode for the RRC instance of each configured SRAT or,alternatively, to release the RRC connection and/or turn off the frontend of each configured SRAT, for example. If HSPA is the PRAT, LTE isthe SRAT and only the HSPA RRC instance may perform the cell reselectionprocedure.

For another example, a state transition in a second RRC instance may notbe allowed depending on the state of a first RRC instance. In anembodiment, an RRC state may not be allowed in an RRC instance for anSRAT based on the current state of another RRC instance. In particular,a WTRU may not transition to a CELL-FACH state or a CELL_PCH state foran HSPA RRC instance if an LTE RRC instance is in an RRC_CONNECTEDstate.

For another example, the operational state of a second RRC instance mayfollow the state of a first RRC instance. In an embodiment, the initialstate of an RRC instance of an HSPA SRAT may be CELL_DCH when the stateof the RRC instance of an LTE PRAT is RRC_CONNECTED.

With respect to transition back to idle mode, a transition to RRC idlefor an RRC connection that is the PRAT of the WTRU may trigger eitherthe release of other RRC connections and/or a move to RRC IDLE foranother RRC instance (e.g., all RATs or only a RAT for which the WTRUshould be in IDLE mode when not connected to the network). The RRCinstance of the PRAT may notify another RRC instance for an SRAT of achange of state to IDLE. The RRC instance for the SRAT may then performthe procedure to move to IDLE mode, remove the dedicated configurationfor the SRAT, revert to the default configuration and/or activate and/orturn off the transceiver module and/or some functionality of the SRAT.

With respect to action upon a PUCCH/SRS release request, the PRAT LTERRC instance may receive an indication to release PUCCH/SRS dedicatedresources from the lower layers (e.g., LTE MAC). This may occur, forexample, upon reaching the maximum number of scheduling request (SR)transmissions on the configured PUCCH resource for SR or if the timingalignment timer (TAT) expires. When the TAT expires, the WTRU no longerhas a valid timing advance and is no longer synchronized for ULtransmissions. In this case, the RRC instance of the PRAT may indicatethe loss of UL synchronization in the PRAT to the RRC instance of anSRAT.

For embodiments that use a single RRC connection for all configured RATs(e.g., embodiments described with respect to FIGS. 3, 4, 5 and 6 above),a WTRU may, for example, receive RRC messages and configurationparameters regarding the SRAT via SRAT IEs that are piggybacked insideRRC PDUs of the PRAT. In this embodiment, a WTRU may multiplex and/ordemultiplex RAT-specific IEs inside the RRC PDU of the single RRCconnection and identify the IE using an explicit identifier (e.g., anidentity of the RRC state machine or SRAT) inside the RRC PDU.

In an embodiment, the RRC message of the PRAT may include an SRATcontainer IE. The SRAT container IE may include the information for theSRAT, which may be processed according to the RRC of the SRAT. Forexample, if the PRAT is LTE, then an HSPA SRAT may be established byincluding a utra-Secondarycell-Container IE. In an embodiment, thepresence of this IE may trigger the initiation of the secondary RAT.

If more than one SRAT may be established, an SRAT type IE and an SRATmessage container IE may be used. The SRAT message container IE maycarry a message specified in another standard as indicated by the SRATtype IE. This container may carry the information and radio parametersrequired for the SRAT to be configured.

For example, a WTRU may be configured such that each group of cellsconfigured for a given RAT is associated with an identity for that RAT.When the WTRU receives an RRC PDU, it may determine with what RAT an IEis associated and, for example, process the RRC PDU according to theapplicable RAT. Similarly, the WTRU may transmit an RRC PDU includingone or more information elements inside the RRC PDU. If, at most, twoRATs are supported, this may be determined implicitly by the presence ofthe IE itself inside the PDU.

For embodiments that use a separate RRC instance for each configured RAT(e.g., embodiments described with respect to FIGS. 5, 6, 7 and 8 above),a WTRU may, for example, receive configuration parameters regarding theSRAT via multiplexing an RRC PDU for the PRAT and SRAT using differentSRB identifiers (SRB_IDs). In an embodiment, a WTRU may multiplex and/ordemultiplex RRC PDUs over the data path and identify the RRC connectionand/or state machine to which the RRC message is applicable based on theradio bearer identity used for the transmission of the RRC PDU.

For example, a WTRU may be configured such that one or more SRBs areassociated with control signaling of a specific RAT, for example, basedon SRB_ID. When the WTRU receives an RRC PDU, it may determine whatradio bearer the PDU is associated with and, for example, apply theproper security context for authentication (if any) and deciphering ifthe WTRU is configured with a RAT-specific security context and/orprocess the RRC PDU using the applicable RRC state machine for theassociated RAT. Similarly, the WTRU may transmit an RRC PDU using theassociated with the applicable RRC state machine.

In an embodiment, the SRBs applicable for an SRAT may be configuredafter security activation and being associated with a given priority.For example, the WTRU may be configured such that the SRBs applicableto, for example, a subset or a type of an HSPA RRC PDU have the same(or, alternatively, a lower) priority than SRB1 for the transport of theHSPA RRC PDUs over the LTE MAC. For example, the WTRU may be configuredsuch that the logical channel(s) applicable to, for example, a subset ora type of LTE RRC PDU are mapped to a specific priority in themultiplexing functionality of MAC-ehs.

For embodiments that use a single RRC instance for all configured RATs(e.g., embodiments described with respect to FIGS. 3 and 4 above), radioresource management may be carried out using one of more of the examplesdescribed below on a condition that the WTRU receives a configurationthat adds at least one serving cell for an SRAT. In such embodiments, aWTRU may have an established RRC connection (e.g. 306 in FIG. 3) with aPRAT.

In an embodiment, the WTRU may add a serving cell for an SRAT whensecurity is activated (e.g., for the PRAT), in which case it may applythe same configuration for integrity protection and ciphering for theaccess stratum when applicable (e.g., when multiple data paths areused).

In an embodiment, a WTRU may receive an RRC message that adds, modifiesor removes at least part of a configuration for at least one servingcell of the SRAT. The WTRU may not successfully apply the concernedconfiguration, in which case it may invalidate the configuration of theconcerned serving cell, remove the configuration of the concernedserving cell, invalidate the configuration for all serving cells of theSRAT, remove the configuration for all serving cells of the SRAT, turnoff the radio front end for the SRAT, indicate to the network that theconfiguration failed and/or terminate the SRAT RRC instance of the SRATRRC connection. In particular, a failure to apply a configuration for anSRAT may not impact the operation and/or the configuration of the RRCconnection for the PRAT. In case of a failure to successfully completean RRC procedure applicable to an SRAT, the WTRU may abort the procedureand revert to the state before the WTRU initiated the procedure for theconcerned SRAT.

When LTE is the PRAT, the RRC instance may perform radio resourcemanagement for an SRAT according to any of the following embodiments. Inan embodiment, the WTRU operation for the PRAT may be according totypical procedures for the concerned RAT. In an embodiment, a WTRU mayperform RLM for configured serving cells of an LTE PRAT, for example,for the PCell. The WTRU may determine, according to the criterion forRLF of a serving cell of the corresponding RAT, that it is experiencingUL RLF on the PCell of the LTE PRAT. The WTRU may perform an RRC statetransition away from RRC_CONNECTED to RRC_IDLE when it determines RLF(DL or UL) for a PCell of an LTE PRAT, in which case it may remove theconfiguration for all serving cells of an HSPA SRAT and/or turn off theradio front end for the HSPA SRAT.

The WTRU may also perform RLM for configured serving cells of an HSPASRAT. The WTRU may determine, according to the criterion for RLF of aserving cell of the corresponding RAT, that it is experiencing UL RLF onthe primary serving cell. On a condition that the WTRU determines UL RLFfor a serving cell of an HSPA SRAT, the WTRU may invalidate theconfiguration of the concerned serving cell, remove the configuration ofthe concerned serving cell, invalidate the random access configurationof the concerned serving cell, remove the random access configuration ofthe concerned serving cell, invalidate the configuration for all servingcells of the HSPA SRAT, remove the configuration for all serving cellsof the HSPA SRAT, turn off the radio front end for the HSPA SRAT,indicate to the network of the UL RLF condition for the concernedserving cell, consider the secondary RAT serving cells as deactivatedand/or terminate the SRAT RRC instance of SRAT RRC connection.

In an embodiment, the WTRU may determine, according to the criterion forRLF of a serving cell of the corresponding RAT, that it is experiencingDL RLF. On a condition that the WTRU determines DL RLF for a servingcell of an HSPA SRAT, the WTRU may invalidate the configuration of theconcerned serving cell, remove the configuration of the concernedserving cell, invalidate the configuration for all serving cells of theHSPA SRAT, remove the configuration for all serving cells of the HSPASRAT turn off the radio front end for the HSPA SRAT and/or indicate tothe network the DL RLF condition for the concerned serving cell.

A WTRU may perform an RRC state transition from LTE RRC_CONNECTED to LTERRC_IDLE, in which case the WTRU may invalidate the configuration forall serving cells of the SRAT, remove the configuration for all servingcells of the SRAT, turn off the radio front end for the SRAT and/orterminate the secondary RAT RRC instance or SRAT RRC connection.

The PRAT LTE RRC instance may receive an indication to release PUCCH/SRSdedicated resources from the lower layers (e.g., LTE MAC). This mayoccur, for example, upon reaching the maximum number of SR transmissionson the configured PUCCH resource for SR or if the TAT expires. When theTAT expires, the WTRU no longer has a valid timing advance and is nolonger synchronized for UL transmissions. In this case, the WTRU mayinvalidate the configuration for all serving cells of the SRAT, removethe configuration for all serving cells of the SRAT, turn off the radiofront end for the SRAT and/or terminate the SRAT RRC instance or SRATRRC connection.

When HSPA is the PRAT, the RRC instance may perform radio resourcemanagement for an SRAT according to any of the following embodiments. Inaddition, the WTRU operation for the PRAT may be according to typicalprocedures for the concerned RAT.

In an embodiment, the WTRU may receive a radio resource reconfigurationmessage that adds a configuration for a first LTE serving cell withconfigured UL resources, and subsequently may initiate a procedure togain UL timing synchronization (e.g., a random access procedure on theUL PRACH resources of the cell). In an embodiment, the WTRU may receivea handover command, which may include a configuration for at least oneLTE serving cell with configured UL resources. The WTRU may, in additionto the initial access to the HSPA target cell, also initiate a procedureto gain UL timing synchronization (e.g., a random access procedure onthe UL PRACH resources of the LTE target cell).

In an embodiment, the WTRU may perform RLM for one or more of theconfigured serving cells of a PRAT, in particular, for the primaryserving cell of the HSPA PRAT. The WTRU may determine, according to, forexample, the criterion for RLF of a serving cell of the correspondingRAT, that it is experiencing UL RLF on the primary serving cell. On acondition that it determines UL RLF for a primary serving cell of anHSPA PRAT, the RRC instance for the HSPA PRAT may receive a firstout-of-synch indication from the physical layer and may refrain fromperforming UL transmissions. If at least one serving cell of the LTESRAT is configured with UL resources and may transmit UL feedbackinformation on the serving cell, then the WTRU may continue anytransmission on the LTE SRAT.

The WTRU may perform an RRC state transition away from CELL_DCH (and/orto CELL_FACH) when it determines RLF (DL and/or UL) for a primaryserving cell of an HSPA PRAT, in which case it may remove theconfiguration for all serving cells of the LTE SRAT, turn off the radiofront end for the LTE SRAT and/or consider the LTE SRAT as deactivatedby an order.

In an embodiment, the WTRU may perform RLM for configured serving cellsof an LTE SRAT. The WTRU may determine, according to the criterion forRLF of a serving cell of the corresponding RAT, that it is experiencingUL RLF on a serving cell of an LTE SRAT, in particular the PCell. On acondition that it determines UL RLF for a serving cell of an LTE SRAT,the WTRU may invalidate the configuration of the concerned serving cell,remove the configuration of the concerned serving cell, invalidate therandom access configuration of the concerned serving cell, remove therandom access configuration of the concerned serving cell, invalidatethe configuration for all serving cells of the LTE SRAT, remove theconfiguration for all serving cells of the LTE SRAT, turn off the radiofront end for the LTE SRAT, indicate to the network the UL RLF conditionfor the concerned serving cell and/or terminate the SRAT RRC instance orSRAT RRC connection.

In an embodiment, the WTRU may determine, according to the criterion forRLF of a serving cell of the corresponding RAT, that it is experiencingDL RLF. On a condition that it determines DL RLF for a serving cell ofan LTE SRAT, the WTRU may invalidate the configuration of the concernedserving cell, remove the configuration of the concerned serving cell,invalidate the configuration for all serving cells of the LTE SRAT,remove the configuration for all serving cells of the LTE SRAT, turn offthe radio front for the LTE SRAT, indicate to the network the DL RLFcondition for the concerned serving cell and/or terminate the SRAT RRCinstance or SRAT RRC connection.

In an embodiment, the WTRU may perform an RRC state transition from aconnected state (e.g., CELL_DCH, CELL_PCH or URA_PCH) to an idle mode,in which case the WTRU may invalidate the configuration for all servingcells of the LTE SRAT, remove the configuration for all serving cells ofthe LTE SRAT and/or turn off the radio front end for the LTE SRAT.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A method of performing wireless communication in a wirelesstransmit/receive unit (WTRU) configured for multi-radio accesstechnology (RAT) operation, the method comprising: the WTRU wirelesslycommunicating information on a first operating frequency according to afirst RAT; and the WTRU wirelessly communicating information on a secondoperating frequency according to a second RAT.
 2. The method of claim 1,wherein the first RAT is one of long term evolution (LTE) and high speedprotocol access (HSPA) and the second RAT is one of HSPA, LTE and WiFi.3. The method of claim 1, further comprising: the WTRU establishing aradio resource control (RRC) connection in the first RAT using an RRCinstance; the WTRU receiving a configuration for at least one servingcell of the second RAT over the RRC connection; the WTRU configuringradio resources for the second RAT using the RRC instance.
 4. The methodof claim 3, wherein, on a condition that the WTRU performs an RRC statetransition on the first RAT from LTE RRC_CONNECTED to LTE RRC_IDLE, theWTRU performs at least one of: invalidating a configuration for allservicing cells of the second RAT, removing the configuration for allserving cells of the second RAT, and turning off a radio front end forthe second RAT.
 5. The method of claim 1, further comprising the WTRUtransmitting and receiving RRC protocol data units (PDUs) of a typecorresponding to the first RAT, the RRC PDUs of the type correspondingto the first RAT including at least one information element (IE)corresponding to the second RAT.
 6. The method of claim 1, furthercomprising: the WTRU establishing a radio resource control (RRC)connection in the first RAT using a first RRC instance; the WTRUreceiving a configuration for at least one serving cell of the secondRAT over the RRC connection; and the WTRU configuring radio resourcesfor the second RAT using a second RRC instance.
 7. The method of claim6, further comprising the WTRU transmitting and receiving PDUs over theRRC connection, each of the PDUs having a signaling radio beareridentifier (SRB_ID) corresponding to one of the first RRC instance andthe second RRC instance.
 8. The method of claim 6, wherein, on acondition that the WTRU performs an RRC state transition on the firstRAT from LTE RRC_CONNECTED to LTE RRC_IDLE, the WTRU performs at leastone of: invalidating a configuration for all servicing cells of thesecond RAT, removing the configuration for all serving cells of thesecond RAT, turning off a radio front end for the second RAT, andterminating the second RRC instance.
 9. The method of claim 1, furthercomprising: the WTRU establishing a first radio resource control (RRC)connection in the first RAT using a first RRC instance; and the WTRUestablishing a second RRC connection in the second RAT using a secondRRC instance.
 10. The method of claim 9, further comprising the WTRUadding a serving cell for the second RRC connection in the second RAT inresponse to security being activated for the first RAT.
 11. The methodof claim 9, further comprising: the WTRU performing radio linkmonitoring (RLM) for a configured serving cell of the first RAT, thefirst RAT being LTE; the WTRU determining whether the configured servingcell of the first RAT is experiencing radio link failure (RLF); on acondition that the WTRU determines that the configured serving cell ofthe first RAT is experiencing RLF, the WTRU performing at least one ofremoving a configuration for all serving cells of the second RAT andturning off a radio front end for the second RAT, the second RAT beingHSPA.
 12. The method of claim 9, further comprising the WTRU configuringmobility management for the second RRC connection based on the first RRCconnection.
 13. A wireless transmit/receive unit (WTRU) configured formulti-radio access technology (RAT) operation, the WTRU comprising: atransceiver configured to: wirelessly communicate information on a firstoperating frequency according to a first RAT, and wirelessly communicateinformation on a second operating frequency according to a second RAT.14. The WTRU of claim 13, wherein the first RAT is one of long termevolution (LTE) and high speed protocol access (HSPA) and the second RATis one of HSPA, LTE and WiFi.
 15. The WTRU of claim 13, furthercomprising a processor configured to establish a radio resource control(RRC) connection in the first RAT using an RRC instance, wherein: thetransceiver is further configured to receive a configuration for atleast one serving cell of the second RAT over the RRC connection, andthe processor is further configured to configure radio resources for thesecond RAT using the RRC instance.
 16. The WTRU of claim 15, wherein thetransceiver is further configured to transmit and receive RRC protocoldata units (PDUs) of a type corresponding to the first RAT, the RRC PDUsof the type corresponding to the first RAT including at least oneinformation element (IE) corresponding to the second RAT.
 17. The WTRUof claim 13, further comprising a processor configured to establish aradio resource control (RRC) connection in the first RAT using a firstRRC instance, wherein: the transceiver is further configured to receivea configuration for at least one serving cell of the second RAT over theRRC connection, and the processor is further configured to configureradio resources for the second RAT using a second RRC instance.
 18. TheWTRU of claim 17, wherein the transceiver is further configured totransmit and receive PDUs over the RRC connection, each of the PDUshaving a signaling radio bearer identifier (SRB_ID) corresponding to oneof the first RRC instance and the second RRC instance.
 19. The WTRU ofclaim 17, wherein the processor is further configured to, on a conditionthat the processor performs an RRC state transition on the first RATfrom LTE RRC_CONNECTED to LTE RRC_IDLE, perform at least one of:invalidating a configuration for all servicing cells of the second RAT,removing the configuration for all serving cells of the second RAT,turning off a radio front end for the second RAT, and terminating thesecond RRC instance.
 20. The WTRU of claim 13, further comprising aprocessor configured to: establish a first radio resource control (RRC)connection in the first RAT using a first RRC instance, and establish asecond RRC connection in the second RAT using a second RRC instance. 21.The WTRU of claim 20, wherein the processor is further configured to adda serving cell for the second RRC connection in the second RAT inresponse to security being activated for the first RAT.
 22. The WTRU ofclaim 20, wherein the processor is further configured to: perform radiolink monitoring (RLM) for a configured serving cell of the first RAT,the first RAT being LTE, determine whether the configured serving cellof the first RAT is experiencing uplink (UL) radio link failure (RLF);on a condition that the processor determines that the configured servingcell of the first RAT is experiencing UL RLF, perform at least one ofremoving a configuration for all serving cells of the second RAT andturning off a radio front end for the second RAT, the second RAT beingHSPA.
 23. The WTRU of claim 20, wherein the processor is furtherconfigured to configure mobility management for the second RRCconnection based on the first RRC connection.